With the general decline in heavy steel manufacturing using large open hearth and basic oxygen furnaces, many minimills and small steel plants that use electric arc furnaces have become more common. These smaller plants and minimills must maintain high efficiency to maintain their competitive edge against the larger, more integrated steel manufacturers.
An electric arc furnace typically includes a melting vessel comprising an upper shell portion, which is defined by a plurality of water-cooled panels, and a lower shell portion that is lined with refractory brick. A removable roof covers the vessel and at least one electrode extends through the roof. The furnace also typically includes a slag door portion defining a slag discharge opening covered by a slag door mounted on the melting vessel. A slag pit or slag pot is positioned underneath the slag discharge opening outside the furnace to collect the poured off slag. The slag discharge opening is important because an operator not only can view the furnace through this opening, but an oxygen lance may also be extended into the melting vessel through the slag discharge opening. This oxygen lance is important for providing the necessary oxygen for combustion. Thus, it is important to maintain this slag door portion clear of scrap.
During charge or loading of an electric arc furnace with scrap metal dumped from an overhead scrap bucket, the scrap falls into the upper shell and lower shell and typically distributes along certain angles, such as 25-45 degrees. Because of this angle, the scrap typically fills the slag door portion of the furnace. This may cause yield losses because as the scrap door is opened, some of the scrap accumulated at this slag door portion falls in the slag pot adjacent to the door. During furnace operation, the scrap accumulated in the area adjacent to the slag door portion causes the scrap discharge opening to become smaller, thereby blocking an operator's view into the furnace and impeding the introduction of an oxygen lance through the slag discharge opening.
Some prior art electric furnaces have been designed to minimize any interference with the entry of the oxygen lance into the slag discharge opening and maintain an operator's view of the melt. For example, in U.S. Pat. No. 4,563,766 to Bick et al., the charging volume of an electric arc furnace is increased with an increased diameter of the melting vessel, without essentially changing the usually provided height of the furnace container with the dimension of the hearth.
In U.S. Pat. No. 4,805,186 to Janiak, et al., the electrodes are offset towards an orifice in which scrap is fed to locate the hottest point forming the melting center of the scrap in the same place where the scrap can be introduced continuously. Thus, the scrap will melt faster and possibly reduce the chance of blockage.
In one prior art technique used by the assignee of the present invention, a scrap diverting panel in the form of a rectangular configured water-cooled panel was positioned above the slag door portion and extended inwardly at a lower portion to form a scrap free area adjacent the slag door portion. This water-cooled panel formed an awning above the slag door portion, in effect, creating a scrap free area, which could receive the oxygen lance a greater distance into the melting vessel. Before the use of this panel, the oxygen lance could not extend very far into the melting vessel because the scrap impeded the oxygen lance through the slag discharge opening. With the panel, the oxygen lance could be inserted into the scrap free area. However, this rectangular configured panel had corners that extended outward away from the inside surface of the melting vessel. These exposed corners increased the chance that a potentially damaging arc would be generated between the electrode and the exposed corners. This electrode arcing between the electrode and corners (as shown in FIG. 1) reduced furnace efficiency, increased energy costs, and reduced electrode life. In addition, the exposed corners of the panel were subject to damage during scrap charging.